youtube reviews are not needed, definitely not for an international multi-million, or even multi-billion dollar company
They actually kinda do help, I mean depending on whos doing the Review.
Lets take Totalbiscuit for Example, Most of his videos get above 100,000 Views. If he says a Game is good, That means around 100,000 more people would buy it meaning the company makes a huge profit off of a single 5 minute video someone made.
Really youtube is one of the best sources for advertising considering the fact that about 80% of the people who have internet access use it.